1. Field of the Invention
The present invention relates to a liquid crystal display device.
2. Discussion of the Related Art
Until recently, display devices have typically used cathode-ray tubes (CRTs). Presently, many efforts and studies are being made to develop various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission displays, and electro-luminescence displays (ELDs), as a substitute for CRTs. Of these flat panel displays, LCD devices have many advantages, such as high resolution, light weight, thin profile, compact size, and low voltage power supply requirements.
In general, an LCD device includes two substrates that are spaced apart and face each other with a liquid crystal material interposed between the two substrates. The two substrates include electrodes that face each other such that a voltage applied between the electrodes induces an electric field across the liquid crystal material. Alignment of the liquid crystal molecules in the liquid crystal material changes in accordance with the intensity of the induced electric field into the direction of the induced electric field, thereby changing the light transmissivity of the LCD device. Thus, the LCD device displays images by varying the intensity of the induced electric field.
The LCD device uses a backlight to supply light to a liquid crystal panel. A cold cathode fluorescent lamp (CCFL) and an external electrode fluorescent lamp (EEFL) are widely used as the backlight. Recently, a light emitting diode (LED) has been used as the backlight.
FIG. 1 is a schematic view illustrating a backlight using LEDs according to the related art.
Referring to FIG. 1, the backlight 40 includes a plurality of LED blocks BLK that each include a plurality of LEDs. The backlight 40 is below a liquid crystal panel to supply light to the liquid crystal panel. This type backlight 40 is referred to as a direct type backlight.
The LEDs of each LED block BLK are connected in series, and connected to a constant-current source circuit CRC. The constant-current source circuit CRC supplies a constant current to the block BLK, and the LEDs of the block BLK thus emit light.
A plurality of constant-current source circuits CRC are generally configured in one multi-channel driving IC. Accordingly, the multi-channel driving IC drives the blocks BLK the number of which corresponds to the number of the channels of the multi-channel driving IC. Therefore, to drive the backlight 40 of the related art, many driving ICs are required.
However, as the size of the LCD device increases or the backlight 40 having high brightness are required, the number of the LEDs should increase. Accordingly, the number of the blocks BLK should increase, and the number of the driving ICs should increase. Therefore, costs for circuit components to drive the LEDs increases.
To reduce the cost, an increase of the number of the LEDs in each block BLK may be considered. However, this causes increase of power consumption.
Further, since the LEDs in each block BLK are driven in common by the same constant-current source circuit CRC, a halo phenomenon increases and contrast ratio is limited. Therefore, display quality is reduced.